Adaptive method for reducing power consumption in a standby mode of a digital radio communication system

ABSTRACT

Disclosed is an adaptive method for reducing power consumption in a standby mode of a digital radio communication terminal. The method comprises the following steps of: calculating the difference of edge timings between a main clock and a low clock; comparing the calculated timing difference with a predetermined difference reference value; and upgrading or downgrading a catnap period according to a result of the step of comparing.

PRIORITY

This application claims priority to an application entitled “THEADAPTIVE POWER SAVING METHOD FOR DIGITAL WIRELESS COMMUNICATION SYSTEMDURING STANDBY MODE” filed with the Korean Industrial Property Office onDec. 30, 2000 and assigned Ser. No. 2000-87188, the contents of whichare hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to a method for reducing powerconsumption in a mobile radio terminal such as a radio telephone, andmore particularly, to a method for reducing power consumption in astandby mode of a radio terminal when the radio terminal is operated ina slotted paging mode in a CDMA (Code Division Multiple Access) radiotelephone system.

2. Description of the Related Art

The slotted paging mode is a form of DRX (Discontinuous Reception)operations for a mobile radio terminal actuated by a battery such as acellular radio telephone. The mobile radio terminal is adapted to radiocommunication with at least one remote base station in the radiotelephone system. In the slotted paging mode, when the radio terminal(also referred to as a mobile station) is in an idle mode (or is not inconversation), the radio telephone is generally in a low power statewithout continuously monitoring a paging channel.

The slotted paging mode is important in the battery life of the radiotelephone. It is an object of operating the slotted mode to reduce theoperating time of a radio apparatus into the smallest amount andinterrupt the power of the radio apparatus as little as possible duringa sleep period. In an idle mode, the radio telephone wakes up only in apreviously allocated slot by the radio telephone system or for treatingcertain other conditions such as a user input.

In returning from the sleep period, the radio apparatus shouldre-acquire an RF (Radio Frequency) link with the base station of theradio telephone system. Acquisition of the link and other operationsincluding communication protocols for such a system are defined in airinterface standards. An example of such a standard may include theTIA/EIA (Telecommunications Industry Association/Electronic IndustryAssociation) IS-95: “Mobile Station-Base Station Compatibility Standardfor Dual-Mode Wideband Spread Spectrum Cellular System.” The IS-95defines a DS (Direct Sequence)-CDMA or CDMA radio telephone system.

In order to re-acquire the RF link, the radio telephone of the CDMAsystem synchronizes with the system time that is maintained by the basestation and a network controller of the CDMA system. The timing for aforward link (base station to mobile station) should be maintained bythe radio telephone in anticipation that the radio apparatus is promptlystarted when an allocated slot is generated. The timing uncertaintiesare modified and the paging channel is acquired to prepare fortreatment.

The synchronization with the forward link includes an alignment of a PN(Pseudorandom Noise) sequence transmitted to a pilot channel by the basestation and a locally generated PN sequence. The transmitted sequencesinclude a “short PN” sequence, which is repeated every 26⅔ ms, and a“long PN” sequence, which is repeated every 41 days. The radio telephoneincludes a sequence generator for generating short and long PN sequencessame as those used by the base station. The radio telephone uses asearcher receiver or other mechanism for aligning the short PN sequencewith that received from the base station. Once the pilot channel isacquired, the radio telephone acquires a synchronizing channel and thepaging channel. Then, the radio telephone correctly demodulates atraffic channel to establish a full-duplex link with the base station.

In the start after the sleep time, the radio telephone synchronizes withthe long PN sequence and the short PN sequence. The PN sequences and aframe boundary are repeated with a logical frequency in the IS-95system. The frame boundary is generated in every third PN roll boundary.The PN roll boundary is defined by a short PN sequence which reverserolls to the initial value thereof. In the mobile station, the short PNsequence and the long PN sequence are defined as a linear sequence. Theshort PN sequence and the long PN sequence are generated by using a LSG(Linear Sequence Generator). The LSG is described as a polynomial, andobtained by using a shift register and an exclusive OR gate. Since theshort PN sequence is repeated only in every 26⅔ ms, the LSG, whenwithdrawing from the sleep state, can be conveniently stopped in aspecific phase of the sequence until the phase has a correlation with asystem PN. Then, the short PN LSG synchronizes with the system timingand starts again.

However, the long PN sequence is repeated only once in every 41 days. Itis unpractical that the long PN generator of the radio telephone isstopped (for example, when entering the sleep state) and then thegenerator is clocked at high speed to catch up the long PN of the systemin the start thereafter.

Since the short PN sequence and the long PN sequence are transmitted bythe system which varies predictably according to time, the PN sequenceacquisition requires that a correct reference time is maintained in themobile station during the sleep mode. A PN sequence can be suitablydetermined for the correlation with the system PN sequence inwithdrawing from the sleep mode. However, maintaining a precise timingreference requires a relatively high power consumption which iscontradictory to the sleep mode designed for low power consumption.

In addition to withdrawing from the sleep mode during the allocatedslot, the radio telephone is also required to start for handling otherasynchronously generated events in the radio apparatus or for respondingto the same. An example of this type of event can include a user inputsuch as pressing a keypad of the radio telephone. The response to suchan input should be prompt without any delay which can be recognized bythe user.

As it is important in the foregoing related art, a technique forreducing power consumption uses a method in which a receiver in astandby mode is activated only at a pre-designated time to perform areceiving operation during a certain time and then returns to the lowpower mode by using the slotted paging mode supported by the system.Here, even in the low power mode, minimum clocking is required for thepurpose of maintaining synchronization with the system beingre-activated and responding to the external input such as an interrupt.

However, while an edge timing should be suitably used in order to usethe low frequency clock, actually a mode operated in a high frequencyclock is present between receiving modes to maintain the correct edgetiming required by the system. Such a mode is referred to as catnap modein the following description. The operation of this catnap mode isdefined with a certain period, and this period is defined via atrade-off according to an experiment.

However, if the operating period of the catnap mode is shorter thanrequired, a loss is caused in power consumption, and if too long, thesystem may not be suitably synchronized in some cases.

SUMMARY OF THE INVENTION

As described hereinbefore, since the catnap mode, which is used for lowspeed clock compensation to reduce power consumption, is fixed with acertain value, unnecessarily high power consumption may take place or onthe contrary abnormal synchronization to the system may take place.

It is therefore an object of the present invention to provide anadaptive method of updating a catnap period so that a stablesynchronization to the system can take place without an unnecessarypower consumption.

According to an embodiment of the invention to obtain the foregoingobject, an adaptive method for reducing power consumption in a standbymode of a digital radio communication terminal is provided. The methodcomprises the steps: calculating the difference of edge timings betweena main clock and a low clock; comparing the calculated timing differencewith a predetermined difference reference value; and upgrading ordowngrading a catnap period according to the result of the step ofcomparing.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a drawing illustrating the block construction of a radioterminal in a radio telephone system according to the invention;

FIG. 2 is a diagram illustrating a general current waveform of a slottedpaging mode and a catnap mode; and

FIG. 3 is a flow chart illustrating a process for calculating anadaptive catnap mode operation period according to an embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described hereinbelow with reference to the accompanying drawings. In the followingdescription, well-known functions or constructions are not described indetail since they would obscure the invention in unnecessary detail.

The present invention is applicable to a digital radio system supportinga slotted paging mode. First, an example of the radio terminal systemand the radio terminal will be described in detail in reference toFIG. 1. The system is exemplified as disclosed in U.S. Pat. No.6,016,312 assigned to Motorola as shown in FIG. 1.

Referring to FIG. 1, the radio telephone system 100 includes a number ofbase stations which are constructed for radio communication with atleast one mobile station including a CDMA radio telephone such as aradio telephone 104. The radio telephone 104 is adapted toreceive/transmit a DS-CDMA signal for communication with a number ofbase stations, including the base station 102. In the disclosedembodiment, the radio telephone system 100 is a CDMA radio telephonesystem that is operated at 800 MHz according to a temporary standardIS-95 of TIA/EIA: “Mobile Station-Base Station Compatibility Standardfor Dual-Mode Wideband Spread Spectrum Cellular System.” In general, theradio system 100 operates according to another CDMA system or anysuitable radio telephone system including a PCS system which is operatedat 1800 MHz.

The base station 102 transmits a spread spectrum signal to the radiotelephone 104. A symbol of a traffic channel is spread by using a Walshcode in a process that is known as Walsh covering. The mobile stationsuch as the radio telephone 104 is allocated with a characteristic Walshcode by the base station 102 so that a traffic channel transmission toeach mobile station perpendicularly intersects every traffic channeltransmission to a different mobile station. The symbol is spread byusing a short PN sequence or code repeated every 26⅔ ms or a long PNsequence or code repeated every 41 days. A communication via an RF(Radio Frequency) link between the base station and the radio telephone104 has the shape of a chip having a velocity of 1.2288 Mega-chips persecond. The chip is a data bit.

The radio telephone 104 includes an antenna 106, an analog front end108, a modem 110, a call processor 112, a timing controller 114, anoscillator 116, a user interface 118 and a battery 150. The battery 150supplies operating power to other components of the radio telephone 104.

The antenna 106 receives an RF signal from the base station 102 andother neighboring base stations. The received RF signal is convertedinto an electric signal by the antenna 106, and then sent to the analogfront end 108. The analog front end 108 includes an RF section 109including circuit devices such as a receiver and a transmitter which canbe powered off in the slotted paging mode. The analog front end 108filters the signal to provide a conversion to a base band signal.

The analog base band signal is sent to the modem 110 where the base bandsignal is converted into a digital data stream for the followingprocess. The modem 110 generally includes a rake receiver and a searchreceiver. The search receiver searches for a pilot signal which isreceived by the radio telephone 104 from a number of base stationsincluding the base station 102. The search receiver despreads the pilotsignal by using a correlator together with a system PN code generated inthe radio telephone 104 by using a local reference timing. The searchreceiver includes at least one sequence generator such as an LSG 120 togenerate the PN code. The modem 110 correlates the locally generated PNcode with the received CDMA signal. The modem 110 detects a systemtiming indicator transmitted by the radio telephone system 100. Inparticular, the modem 110 detects a PN roll over boundary and sends anindication of the PN roll over boundary to the timing controller 114.The modem also includes a circuit device for transmitting data from theradio telephone 104 to a base station such as the base station 102. Themodem 110 can be constructed of conventional elements.

The call processor 112 controls functions of the radio telephone 104.The call processor 112 is operated in response to a stored commandprogram, and includes a memory for storing commands and other data. Thecall processor 112 includes a clock input 122 for receiving a clocksignal and an interrupt input 124 associated with the timing controller114 for receiving an interrupt request signal. The call processor 112receives an interval from the base station 102, in which the radiotelephone should search for a page. The radio telephone can monitor thepaging channel for 160 ms during this interval, but cannot be in a sleepstate. The call processor 112 adjusts an event in the radio telephonerequired for entry and exit into/from the sleep mode. Such an eventincludes steps of continuously tracing a system time, proceeding to theLSG state, restarting the oscillator 116, enabling power to the RFsection 109 of the analog front end 108 and restarting the clock fromthe timing controller 114 to the modem 110. The call processor 112 isassociated with other elements of the radio telephone.

The user interface 118 allows the user to control the operation of theradio telephone 104. The user interface 118 typically includes adisplay, a keypad, a microphone and a receiver. The user interface 118is associated with the call processor 112 by a bus 152.

The timing controller 114 controls the timing of the radio telephone104. In particular, the timing controller 114 controls an entry/exitinto/from the slotted paging mode by the radio telephone 104 and asynchronization of the local timing of the radio telephone 104 with thesystem timing of the radio telephone system 100. The timing controller114 has a clock input 130 for receiving a clock signal from theoscillator 116, an interrupt input 131 for receiving an interruptrequest from the user interface 118 and an interrupt input 132 forreceiving an interrupt request from other components of the radiotelephone 104.

The timing controller 114 has a timing input 134 for receiving thetiming signal from the modem 110 and a timing output 136 for sending thetiming signal to the modem 110. The timing signal (designated as“PNSTROBE” in FIG. 1) received from the modem 110 corresponds to a PNroll boundary of the short PN sequence of the radio telephonesynchronized to the base station. The PN roll boundary is defined in areturn of the PN sequence as the initial value. “PNSTROBE” is a seriesof pulses every 26⅔ ms, which are synchronized to the PN roll boundary.The timing signal (designated as “CHIPX8” in FIG. 1) sent to the modem110 is a clock signal of a velocity of 8×1.2288 Mega-chips per second.Other suitable velocities can also be used. When the timing signal iscleared from the modem 110, the modem 110 enters the low power mode andthe entire internal state is frozen.

The oscillator 116 is a reference oscillator for generating a referenceclock signal at a first velocity. In the disclosed embodiment, theoscillator 116 generates a precise clock signal having accurateresolution such as a clock signal of 16.8 MHz. The timing controller 114has a control output 138 for sending a control signal to the oscillator116. In response to the control signal, the oscillator 116 is activatedand inactivated. When inactivated, the oscillator 116 enters the lowpower mode. The timing controller 114 further sends the control signal(designated as “RXCTRLB” in FIG. 1) to the analog front end 108. Inresponse to the control signal, the analog front end 108 is selectivelypowered off.

In such a method for reducing power consumption of the radio telephone104 of the radio telephone system, a certain period has been given tothe catnap mode so far which operates in the high frequency clock, evenin the receiving mode, to maintain a correct edge timing as required bythe system to suitably use the edge timing with the low frequency clock.

Referring to FIG. 2, the operation of the catnap mode 301 has beendefined with a certain period so far, which is determined through atrade-off by an experiment. It can be seen that power is consecutivelyconsumed in a conversation mode 300 as shown in FIG. 2.

The present invention adaptively adjusts the operating period of thecatnap mode to prevent that the operating period of the catnap mode fromhaving a power consumption loss if in practice, the operating period ofthe catnap mode is shorter than necessary or the operating period of thecatnap mode is not suitably synchronized to the system if too long.

FIG. 3 is a flow chart illustrating a process for calculating anadaptive catnap mode operation period according to an embodiment of theinvention. Such an operation can be performed by the timing controller114 of the radio telephone 104. Referring to FIG. 3, variables necessaryfor calculation are determined and a reference calculation is performed.In the operation, the difference between edge timings of a main clockand a low frequency clock are counted and then stored in a variable“DIFF.” Also, a period T of the catnap is determined for the applicationduring the present slot cycle. Such a period T can be suitablypredetermined in the initial stage. Then, a variable “TTEMP” isdetermined for the catnap period calculation of the next step. SFI(Scaling Factor for Increment) and SFD (Scaling Factor for Decrement)are scaling vectors used in adaptively upgrading or downgrading the“TTEMP”, and both are determined by the period of the catnap.

In step 402, it is determined if the edge timing difference “DIFF” ofthe main clock and the low frequency clock calculated above is over apredetermined difference reference value “DA (Difference Allowed).”Being over the difference reference value “DA”, the process proceeds toupgrade the catnap period calculation variable “TTEMP” by using thedifference value “DIFF” and “SFI” in step 403, which is followed byproceeding to step 405. Conversely, if the edge timing difference “DIFF”is less then or equal to the predetermined difference reference value“DA” in step 402, the process proceeds to downgrade the “TTEMP” by using“DIFF” and “SFD” in step 404, which is also followed by proceeding tostep 405. Steps 402 to 404 are repeatedly calculated in the catnapgenerated in the low power mode during one slot cycle.

In step 405, a calculated result is compared to a predetermined value asthe maximum critical value “TU.” If the calculated result is greaterthan the maximum critical value “TU”, the process proceeds to step 406to shorten the catnap period “T” to prevent any unsuitablesynchronization to the system. Conversely, if the calculated result isless than or equal to the maximum critical value “TU”, the processproceeds to step 407. In step 407, the calculated result is comparedwith a predetermined value as the minimum critical value “TL.” If thecalculated result is less than the minimum critical value “TL”, theprocess proceeds to step 408 to lengthen the catnap period “T” to reducean unnecessarily consumed current. In step 409, the “TTEMP” isinitialized. The process is then repeated by returning to step 401.

In the foregoing construction according to the digital radiocommunication terminal system of the present invention, the reducingoperation of adaptive power consumption can be performed in a standbymode. As described hereinbefore, the invention can adaptively adjust theperiod for suitable system synchronization which is necessary for thelow power mode required by the digital radio mobile terminal therebyhaving effects to suitably adjust the system synchronization andoptimize the consumed current as well according to the system state.

While the invention has been shown and described with reference to acertain preferred embodiment thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. An adaptive method for reducing power consumption in a standby modeof a digital radio communication terminal, comprising the steps of: (A)calculating the difference of edge timings between a main clock and alow frequency clock; (B) comparing the calculated timing difference witha predetermined difference reference value; (C) upgrading or downgradinga catnap period calculation variable according to a result of step (B);(D) comparing the upgraded or downgraded catnap period calculationvariable with predetermined maximum and minimum critical values; (E)shortening or lengthening the catnap period according to a result ofstep (D); (F) comparing the catnap period calculation variable with thepredetermined maximum critical value; (G) shortening the catnap periodif the catnap period calculation variable is greater than the maximumcritical value; (H) comparing the catnap period calculation variablewith the predetermined minimum critical value if the catnap periodcalculation variable is less than or equal to the maximum criticalvalue; and (I) lengthening the catnap period if the catnap periodcalculation variable is less than the minimum critical variable.